Wireless Network With Multiple Paths Between Nodes

ABSTRACT

A wireless communications system includes both a primary communications path wherein a gateway can communicate with each member of a plurality of ambient condition detectors, and a secondary back-up path available in the event of a failure on part of the primary path. Required power for the network can be minimized by path selection.

FIELD

The application pertains to wireless, or, mesh networks. More particularly, the application pertains to such networks which provide multiple links between a gateway and the various displaced nodes, or devices.

BACKGROUND

A wireless network is a system whose devices communicate each other through radio waves, without using cables. The network basic element is called node, and the root node is typically referred to as the gateway. This gateway is the main interface between the wireless network and an external system, which is typically an existing wired fire system handled by a panel.

The gateway is in charge to translate the messages traveling between wired (panel) and wireless (nodes) domains, in order to make the wireless nodes “attached” to it, visible to the panel as if they would be physically connected to the wired network. All wireless devices but the gateway are battery powered, therefore the current consumption will preferably be kept to the lowest possible level in order to maximize devices' lifetime.

A node typically consumes most of the power while communicating with other nodes; the most power saving configuration (topology) is the star as illustrated in FIG. 1, in which the number of links of every single node is limited to the minimum required to meet network constraints.

The star configuration can only be used if the communication link (both physical distance and obstacles) between nodes and the gateway is good enough to allow for a direct link between every single node and the gateway. Moreover, it's necessary that all nodes are able to establish a good-enough link with at least one other node, in order to guarantee that a secondary path is always available. In most cases not all nodes are able to communicate directly with the gateway, therefore they communicate with the node closest to them, which in turn will forward the received information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a star network;

FIG. 2 is a diagram of an initial embodiment in accordance herewith;

FIG. 3 is a diagram of another embodiment in accordance herewith;

FIG. 4 illustrates aspects of a process in accordance herewith;

FIG. 5 illustrates further aspects of the process from FIG. 4;

FIG. 6 illustrates exemplary primary path and node physical addresses;

FIG. 7 illustrates additional aspects of the process from FIG. 4;

FIG. 8 illustrates slot allocation results relative to a network;

FIG. 9 illustrates a network having both a primary path and a secondary path;

FIG. 10 illustrates where a node cannot be contacted through a secondary path

FIG. 11 illustrates a network with an incomplete secondary path;

FIG. 12 illustrates the network of FIG. 10 with a complete secondary path;

FIG. 13 illustrates the primary path of a network created using an alternate way meeting the double path constraint; and

FIG. 14 illustrates a secondary path for the network of FIG. 13.

DETAILED DESCRIPTION

While disclosed embodiments can take many different forms, specific embodiments hereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles hereof, as well as the best mode of practicing same, and is not intended to limit the claims hereof to the specific embodiment illustrated.

In embodiments hereof, a wireless system functions reliably even if one of its nodes fails to transmit its information. As discussed below, such information, from an originating node, will have at least two paths, or links to reach a gateway. FIG. 2 illustrates an exemplary mesh configuration 20 in which each node N is able to communicate with, or, reach the rest of the network through at least two different paths.

In FIG. 2, the path(s) labeled R are primary paths. The path(s) labeled G are secondary paths. The noted paths correspond to wireless communications paths. The gateway, which might be coupled to and communicate with an alarm monitoring system, is labeled W. A plurality of nodes, labeled N can communicate with the gateway via at least two different paths or communications links. Nodes can be implemented as ambient condition detectors of all types, alarm indicating output devices, or any other type of useful module without limitation.

For each node N, the node that precedes it in a primary path is called primary parent, and the one that follows is called primary child. The same concept applies to the secondary path. The primary path(s) always originates from the gateway W. Each node has typically a physical address, normally settable by a switch, and a network address, hereafter called a slot address, by which the node is recognized during the wireless communication process.

As explained below, the present process generates slots, or slot addresses, for nodes of a mesh wireless network that complies with the following constraints:

a) The gateway W is always allocated at the lowest slot (i.e. slot 0);

b) The slot of a node N must be greater than the slot of its primary and secondary parents;

c) The slot of a secondary parent of a node N must be greater than the slot of the primary parent;

d) All nodes must have both a primary and secondary parent, when not in contradiction with constraints b) and c);

e) The slot address of the nodes N must increase in response to moving away from the gateway W;

f) The gateway W is allowed to have all the network nodes N as its primary children;

g) Each node other than the gateway is allowed to have at most 2 primary children;

h) Each node other than the gateway is allowed to have at most 4 children (as the sum of primary and secondary);

i) The communication between two nodes can take place only at a distance less than a constant dMax, where dMax is a calculated value taking into account the physical distance between nodes and the radio attenuation factors (e.g. typical environmental noises, and/or obstacles) in other words dMax is adjusted in order to take into account other factors related to the installation environment, therefore becoming something like a “radio” distance;

j) All nodes that are within the dMax distance from the gateway, must have the gateway as primary parent.

This also implies that:

k) There is always be one node which cannot have the secondary parent, and:

-   -   1. This node must be allocated at slot 1;     -   2. This node primary parent must be the gateway (slot 0);

l) If available, the node allocated at slot 2 have always the following parents:

-   -   1. The gateway (slot 0) as primary parent;     -   2. The node allocated at slot 1 as secondary parent.

As a prerequisite, each node must be within the distance of dMax from at least one other node. If the network doesn't comply with the prerequisite, it's mandatory to add one or more nodes in such positions as to meet constraints.

FIG. 3 illustrates an exemplary network 30 that complies with constraints. Numbers in boxes indicate the slot address of the respective node.

The process can be logically divided into three parts:

1. Primary path definition

2. Slot allocation

3. Secondary path creation

A more detailed description follows. Primary path definition connects all nodes to the gateway by establishing the primary path. In order to optimize power consumption, the gateway's children number is maximized. During this step all nodes are assigned a level, indicating the number of intermediate nodes between the examined one and the gateway W.

With respect to FIG. 4 and partial network 40 thereon, the nodes N1 that are within the circle of radius dMax centered at the gateway W, are assigned a level of 1, indicated as L1. These nodes shall be directly connected to the gateway W.

For each node with level=1 (L1), search for the two closest unassigned nodes but always within the predetermined distance dMax and connect them to the node. Then assign those nodes a level of 2 (L2).

The above process is repeated for each level greater than 1. A primary path is then obtained, as illustrated in FIG. 5.

FIG. 6 illustrates a network 60. The numbers inside the respective squares indicate a node's physical address. This address is not related to the assigned slot, logical address.

Next, to carry out slot allocation, with respect to FIG. 7 and network 70 illustrated therein, a system of orthogonal Cartesian axes centered in the gateway W is established. For each node, the angle (measured counterclockwise) between the X axis and a line connecting the center of the node with the origin of the axis is identified.

Given node's levels and angles, slots are then assigned from 1 to n from the node at level 1 having the lowest angle to the node at last level having the highest angle. This way, slot 1 is allocated to the node at level 1 having the smallest angle, slot 2 to the node at level 1 having the second smallest angle and so on. When all nodes at level 1 are allocated, the same procedure is applied to the other levels until all nodes have been allocated.

FIG. 8 shows the slot allocation result applied to the analyzed network 60 for example. In FIG. 8, the numbers inside respective squares indicate the node's slot address.

The slot address 0 is assigned to the gateway W. Given allocation of the slot addresses, as in FIG. 8, a secondary path meeting constraints can be created by connecting branches close together.

With respect to FIG. 9, and illustrated network 60, In order to create a secondary path, it's enough to connect the nodes—starting from the one allocated at slot 1—to the closest “unconnected” node, and continue until all the nodes are connected. At the end a path in a spiral shape is created. This shape is the one that minimizes the length of the branches of the path.

For some spatial arrangements of the nodes, as illustrated by network 80 in FIG. 10, alternate processing is required to generate a complete secondary path. In the case of network 80, it may not be possible to reach a node through a secondary path.

In FIG. 11 the node N2 with slot=4 cannot have a secondary parent with slot<4 and slot>3 (constraints b, c, d). In such a scenario, to be able to create the secondary path, it is necessary to apply a variant of the algorithm.

This variant includes swapping the slots (in pairs) of the nodes of lower level than the level of the node that it was not possible to reach with the secondary path. Although this operation doesn't change the primary path, it allows building a complete secondary path. In the illustrated example of FIG. 12, the unreachable node is at level 2, by swapping the slots 2 and 3—both at level 1 —, a complete secondary path meeting network constraints is achieved as illustrated in FIG. 12.

Moreover, even if the variant is unable to create the secondary path, there is a final solution which allows to always creating both primary and secondary paths. Nevertheless, it's important to note that this solution is not optimal from the power consumption point of view, since it connects only two nodes to the gateway.

Starting from the gateway W, create two chains with the same number of nodes as primary path as in network 82 of FIG. 13. Then, assign even slots to one chain and odd slots to the other. The secondary path will then be created by connecting every node of the network 82, as shown in FIG. 14.

More generally, the process includes:

a. Creating the two chains with the same number of nodes, as primary path as in FIG. 13;

b. Assigning the nodes of the first chain (C₁) the even slots;

c. Assigning the nodes of the second chain (C₂) the odd slots;

d. Creating secondary path.

Given S the slot number assigned to a node, L(x, y) the link between a node assigned at slot x (parent) and the one assigned at slot y (child), provides the basic constraints for nodes allocated at slots 1 and 2. This kind of network is generated by applying the following rules to each node of the network:

Primary Path use L (S, S+2) and Secondary Path use L (S, S+1)

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Further, logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be add to, or removed from the described embodiments. 

1. A method comprising: establishing a selected distance parameter; assigning an initial slot address to the gateway; and establishing a primary path by determining those nodes closest to the gateway according to the devices' relative distances and installation site's environmental peculiarities, and assigning an incremented level value to each such current node, for each current node with an incremented level with a value of one greater than the gateway's one, search for the two closest unassigned nodes using the same distance evaluation criteria and connect them to the current node and then assign those nodes a level one greater than that of the current nodes, and repeating the process till all nodes are assigned a level value.
 2. A method as in claim 1 which includes assigning slot addresses to the various nodes.
 3. A method as in claim 2 wherein slot addresses are assigned to all nodes at a common level, before addresses are assigned to nodes at an increased level.
 4. A method as in claim 3 which includes creating a secondary path between each of the nodes and the gateway.
 5. A method as in claim 4 where creating a secondary path includes connecting each of the nodes to a closest unconnected node until all the nodes are connected.
 6. A method as in claim 5 wherein connecting the nodes comprises creating a spiral shaped path which minimizes the length of the branches of the path.
 7. A communications system comprising: a gateway unit; and a plurality of secondary units wherein the secondary units communicate with each other, at least in part, and the gateway unit by at least two different communications paths wherein a length parameter of one of the paths minimizes the length of the branches of the path.
 8. A communications system as in claim 7 wherein paths are selected to have a length less than or equal to a predetermined distance related parameter.
 9. A communications system as in claim 8 wherein paths are selected to have a length less than or equal to an adjusted distance related parameter taking into account the environmental site peculiarities included, but not limited to, radio attenuation and/or typical electromagnetic noises.
 10. A communications system as in claim 7 wherein the secondary units and the gateway communicate wirelessly.
 11. A communications system as in claim 7 where the secondary units are battery powered.
 12. A communications system as in claim 11 where the distances between units are selected so as to minimize power consumption.
 13. A communications system as in claim 7 where the secondary units comprise, at least in part, ambient condition detectors.
 14. A wireless communications system as in claim 7 where the gateway comprises a wireless interface for an alarm monitoring system. 